The conventional nuclear magnetic resonance imaging (MRI) device is provided on the periphery of an object to be imaged with a magnet for generating a static magnetic field and a gradient magnetic field which is varying temporal and spatial magnetic field intensity (gradient coil), and is consequently enabled to form a spatially uniform magnetic field with the gradient coils. The magnetic resonance imaging is an operation of applying a radiofrequency (RF) wave to an object to be imaged for the purpose of magnetic resonance in a static magnetic field B0 and consequently encoding and imaging the phase and the frequency of a spin in the magnetically resonating atomic nuclei. For the sake of reducing the spatial distribution of the density and the chemical structure of a resonant element, for example, to an image, an gradient magnetic field having spatially varying magnetic field intensities in the x, y and z directions is superposed. Meanwhile, the technique for heightening the speed (shortening the imaging time) results in curtailing the time for instrumentation. Various methods for high speed and ultrahigh speed imaging have been hitherto proposed and applied for patent. They include the gradient recalled echo (GRE) method, the fast field echo (FE) method, the echo planar imaging (EPI) method, the spiral fast imaging, spiral scan (SPI) method and the single-excitation spin echo (SE) method, for example.
The time required for imaging a two-dimensional image in the conventional technique is in the range of several seconds to some tens of seconds (GRE method), 0.1 to several seconds (EPI method and SPI method) and 0.02 to several seconds (single-excitation SE method) when the image consists of 128 by 128 pixels. When the three-dimensional image consists of 128 by 128 by 128 pixels these ranges are each increased to some tens to 100 times those mentioned above. This time requirement thus has posed a problem.
This invention has its principle based on nuclear magnetic resonance similarly to the conventional techniques and makes it possible to visualize the state (structure and function) in the two-dimensional and three-dimensional spatial distribution in an object to be imaged and the temporal change thereof. It is aimed at providing a device which, by predicting the temporal and spatial operation of an object to be imaged, thereby decreasing greatly the numbers of phase encodings and frequency encodings, is enabled to accomplish such a remarkable increase of speed as has never been attained by the conventional technique.
(1) Improvement of Temporal Resolution in Consequence of Increased Speed of Imaging
The alleviation of a burden on an object to be imaged (the decrease of the time bound by imaging), and the exaltation of the temporal resolution in the imaging are attained in consequence of the increase of speed (the decrease of the imaging time). On the other hand, the increase of the number of dimension results in increasing the amount of information to be obtained.
(2) Imaging of Object in Motion (Reduction of Temporal Change to Image)
The internal changes of an object to be imaged (chemical changes and reactions and physical changes of flows and deformations), which are occurring in a brief duration of time as compared with the imaging time attained by the existing technique, are comprehended. The spatial changes of a spin originating in a magnetic resonance element existing within a two-dimensional plane (x, y) are acquired and displayed in a three-dimensional image (x, y, t), The spatial displacements of a spin originating in a magnetic resonance element existing within a three-dimensional structure (x, y, z) are collected and displayed in a four-dimensional image (x, y, z, t).